1. Field of the Invention
The invention relates to a RFID (Radio-Frequency IDentification) system, and more particularly to a RFID system which binary-searches a number space of each of responders to thereby identify a responder(s) existing in a communication area in which an interrogator can make communication with the responder(s).
2. Description of the Related Art
A RFID system has been conventionally used for controlling communication made between each of a plurality of responders each of which has a unique identification number, and makes a response in radio-frequency communication to an inquiry transmitted from a later mentioned interrogator, and an interrogator which makes an inquiry to each of the responders, and receives the response from each of the responders, and further for identifying a responder or responders existing in a communication area in which the responders and the interrogator can make communication with each other. Each of the responders is fabricated in a quite small size by means of a semiconductor integrated circuit chip, and is designed to be able to operate even by power extracted out of received radio-signals. Such a responder is called a non-contact type IC card, an IC tag, a radio-wave tag or a transponder, for instance, and is attached to or held with an object to be identified.
FIG. 1 is a block diagram of a conventional RFID system.
The illustrated RFID system is comprised of a plurality of responders 103 to 106, an interrogator 20, and a host computer 30.
Each of the responders 103 to 106 is fabricated in a quite small size by means of a semiconductor integrated circuit chip, and is designed to be able to operate even by power extracted out of received radio-signals. Each of the responders 103 to 106 stores therein an identification number unique thereto, and receives an inquiry from the interrogator 20 in radio-frequency communication through a built-in antenna which inquiry includes search conditions for designating a communication area in which a number area of an identification number is to be searched. If an identification number of a responder matches to the search conditions, the responder transmits a response to the interrogator 20. Then, the responder receives an instruction from the interrogator 20 to inactivate the responder, and thus, inactivates a response to be transmitted therefrom.
It is assumed in the explanation made hereinbelow that the responders 103 to 106 store therein 3-bit identification numbers 001, 011, 101 and 110 unique thereto, respectively, and exist in a communication area R0 in which the interrogator 20 can make radio-signal communication with the responders 103 to 106.
The interrogator 20 receives inquiry data including search conditions, from the host computer 30, and transmits an inquiry based on the received search conditions to each of the responders 103 to 106 in radio-frequency communication. The interrogator 20 receives and detects a response transmitted from the responder 103, 104, 105 or 106 having an identification number matching to the search conditions, and transmits the thus detected response to the host computer 30. Then, the interrogator 20 transmits an instruction to a responder having an identification number matching to the search conditions, based on the inquiry data received from the host computer 30, for inactivating the responder.
The interrogator 20 is sometimes called a scanner, a reader or a radio-signal station.
A program for carrying out radio-frequency identification is installed as a control program in the host computer 30, and thus, the host computer 30 has a function of acting as a discriminator which function is accomplished by software. The host computer 30 (a) controls communication made between a plurality of the responders 103 to 106 and the interrogator 20, (b) transmits inquiry data including search conditions to the interrogator 20, (c) causes the interrogator 20 to transmit an inquiry based on the search conditions, to the responders 103 to 106, (d) transmits an instruction to the responders 103 to 106 to inactivate the responders 103 to 106, and (e) judges whether response numbers received from the responders 103 to 106 are in collision with one another, based on a detection signal output from the interrogator 20, for binary-searching number spaces of the identification numbers to identify a responder or responders existing in the communication area R0 among the responders 103 to 106.
FIG. 2 is a block diagram of a RF block of the interrogator 20 as a part of the RFID system illustrated in FIG. 1.
The RF block of the interrogator 20 is comprised of a signal-receiving antenna 200, a signal-transmitting antenna 201, a first band pass filter (BPF) 202, a power amplifier 203, a modulator 204, an oscillator 205, a second band pass filter 206, a phase shifter 207, a first synchronism detector 208, a first low pass filter 209, a second synchronism detector 210, and a second low pass filter 211.
The oscillator 205 transmits a reference signal to the modulator 204, the first synchronism detector 208, and the second synchronism detector 210.
The modulator 204 receives the reference signal from the oscillator 205 and the inquiry data from the host computer 30. The modulator 204 modulates the reference signal in accordance with the inquiry data, and transmits the thus modulated signal to the power amplifier 203.
The power amplifier 203 amplifies the modulated signal received from the modulator 204, and transmits the thus amplified signal to the first band pass filter 202.
The first band pass filter 202 receives the amplified signal from the power amplifier 203, and restricts a frequency-band of the received signal into a predetermined frequency. Then, the signal is radiated into air as radio-signals through the signal-transmitting antenna 201.
The signal-receiving antenna 200 receives radio-signals, and transmits the received radio-signals to the second band pass filter 206.
The second band pass filter 206 restricts a frequency-band of the received signal into a predetermined frequency, and transmits the signal to the phase shifter 207.
The phase shifter 207 converts a phase of the received signal by 90 degrees, and transmits the originally received signal to the first synchronism detector 208 and the phase-converted signal to the second synchronism detector 210.
The first synchronism detector 208 synchronously detects the signal received from the phase shifter 207, based on the reference signal received from the oscillator 205, for extracting a signal having a necessary frequency. The thus extracted signal is transmitted to the first low pass filter 209. Similarly, the second synchronism detector 210 synchronously detects the phase-converted signal received from the phase shifter 207, based on the reference signal received from the oscillator 205, for extracting a signal having a necessary frequency. The thus extracted signal is transmitted to the second low pass filter 211.
The first low pass filter 209 restricts a frequency band of the signal received from the first synchronism detector 208 into a predetermined frequency, and transmits the thus restricted signal to the host computer 30 as the detection signal. Similarly, the second low pass filter 210 restricts a frequency band of the signal received from the second synchronism detector 210 into a predetermined frequency, and transmits the thus restricted signal to the host computer 30 as the detection signal.
FIG. 3 is a flowchart showing steps to be carried out by the host computer for radio-frequency identification in the RFID system illustrated in FIG. 1.
First, search conditions which designate a communication area in which a number space of an identification number is searched are initialized for turning all bits into indefinite bits X, and all of number spaces are designated, in step S2.
Then, the host computer 30 causes the interrogator 20 to transmit an inquiry made based on the search conditions, to the responders 103 to 106, in step S3.
Then, the host computer 30 causes the interrogator 20 to receive responses from a responder or responders having an identification number matching to the search conditions, in step S4.
Then, the host computer 30 judges whether response numbers received by the interrogator 20 are in collision with one another, in step S5.
If the response numbers are in collision with one another (YES in step S5), a bit which is not in collision with a bit in another response number remains unchanged, and a bit which is in collision with a bit in another response number is reset into a fixed binary number 0 or 1, in step S6. Then, the above-mentioned steps S3 to S5 are repeatedly carried out.
If the response numbers are not in collision with one another (NO in step S5), the host computer 30 stores therein the response number comprised of the identification number of the responder 103, 104, 105 or 106 which exists in the communication area R0, in step S7.
Then, the host computer 30 causes the interrogator 20 to transmit an instruction to the thus identified responder to inactivate itself, in step S8.
Then, the host computer 30 judges whether binary-searching is completed in each of number spaces, in step S9. If completed (YES in step S9), the process of identifying a responder or responders existing in the communication area R0 is finished. If not completed (NO in step S9), the above-mentioned steps S6, S3 to S5, and S7 to S9 are repeatedly carried out.
A detailed operation of the conventional RFID system is explained hereinbelow with reference to FIGS. 1 to 3. It is assumed in the explanation made hereinbelow that the responders 103 to 106 store therein 3-bit identification numbers 001, 011, 101 and 110 unique thereto, respectively, and exist in the communication area R0 in which the interrogator 20 can make radio-signal communication with the responders 103 to 106.
With reference to FIG. 3, the 3-bit search conditions are initialized or reset to turn all of the bits into indefinite bits X, in step S2. Thus, there is obtained the search conditions XXX.
Then, the host computer 30 causes the interrogator 20 to transmit an inquiry made based on the search conditions XXX, to the responders 103 to 106, in step S3.
Since the responders 103 to 106 have the identification number 001, 011, 101 and 110, respectively, matching to the search conditions XXX, the responders 103 to 106 transmit their identification numbers as response numbers to the interrogator 20 in response to the inquiry transmitted from the interrogator 20, in step S4.
As a result, there occurs collision in all of bits 2, 1 and 0 in the response numbers which the interrogator 20 received (YES in step S5). Hence, the host computer 30 newly determines the search conditions, in step S6. Specifically, the bit 2 is changed to a fixed binary number 0, and thus, there is obtained newly determined search conditions 0XX.
Then, the steps S3 to S5 are carried out again. Specifically, the host computer 30 causes the interrogator 20 to transmit an inquiry made based on the search conditions 0XX, to the responders 103 to 106, in step S3.
Since the responders 103 and 104 have the identification number 001 and 011, respectively, matching to the search conditions 0XX, the responders 103 and 104 transmit their identification numbers as response numbers to the interrogator 20 in response to the inquiry transmitted from the interrogator 20, in step S4.
As a result, there occurs collision in the bit 1 in the response numbers which the interrogator 20 received (YES in step S5). Hence, the host computer 30 newly determines the search conditions, in step S6. Specifically, the bits 2 and 0 remain unchanged, and the bit 1 is changed to a fixed binary number 0. Thus, there is obtained newly determined search conditions 00X.
Then, the steps S3 to S5 are carried out again. Specifically, the host computer 30 causes the interrogator 20 to transmit an inquiry made based on the search conditions 00X, to the responders 103 to 106, in step S3.
Since only the responder 103 have the identification number 001 matching to the search conditions 00X, the responder 103 transmits its identification number as a response number to the interrogator 20 in response to the inquiry transmitted from the interrogator 20, in step S4.
Thus, there occurs no collision in the bits 2, 1 and 0 in the response number which the interrogator 20 received (NO in step S5).
Then, the host computer 30 stores therein the response number comprised of the identification number 001 of the responder 103 as an identification number of a responder existing in the communication area R0, in step S7.
Then, the host computer 30 causes the interrogator 20 to transmit an instruction to the responder 103 not to respond to inquiries which the interrogator 20 will transmit, in step S8.
Since all of the identification numbers are not identified yet (NO in step S9), the host computer 30 newly determines the search conditions, in step S6. Specifically, the bit 1 which has been previously changed into a fixed binary number 0 due to the collision is changed to a fixed binary number 1. Thus, there is obtained newly determined search conditions 01X.
Thereafter, the steps S3 to S9 are repeated carried out until the responders 104, 105 and 106 are all identified and inactivated. Thus, identification of all of the responders 103 to 106 existing in the communication area R0 is finished.
Table 1 shows a relation among the search conditions, the response number or the identification number which the interrogator 20 received, a bit at which collision occurs, and the identified responder.
TABLE 1InquiryBit at whichTransmissionSearchReceived ResponseCollisionIdentifiedNo.ConditionsNumberoccursResponder1XXX001, 011, 101, 1102, 1, 020XX001, 0111300X001103401X01110451XX101, 1101, 0610X101105711X110106ALL
As an example of a conventional RFID system, Japanese Patent No. 3051561 has suggested a non-contact type IC card system in which a responder is attached to a mobile. The system is designed to include a controller which detects a signal received from the non-contact type IC card, and applies feedback control to power transmitted from a radio-signal station such that the detected signal is constant. When the controller receives a final signal from the non-contact type IC card, the controller transmits a control signal to the radio-signal station to reset power transmitted from the radio-signal station. As the mobile is located closer to the radio-signal station, a communication area in which the mobile can make communication with the radio-signal station becomes narrower. This ensures that other mobiles are out of the communication area, and thus, avoids radio interference. Thus, the radio-signal station can start making communication with next mobile, after the completion of communication with the previous mobile.
When a plurality of responders, such as a non-contact type IC card, an IC tag, a radio-signal tag or a transponder, each attached to or held in a mobile exists in a communication area in which the responders and an interrogator can make communication with each other, and moves fast, a RFID system is required to identify very rapidly and at real-time all of the responders existing in the communication area for the purpose of optimal processing. Even if the responders do not move fast, if a lot of responders exist in the communication area, a RFID system is required to do the same.